If you mean what is the difference between a Grade II and a Grade III:
the engraving on the Grade II from 1956 until 1962 consisted of two prarie dogs on the right side and two squirrels in a tree on the left side. in addition there is a lone duck in flight on the top of the receiver. These all had the coin finish.
From 1962 until the end of Belgian production the engraving patternis the same, except reversed. The lone duck is still present on the top of the receiver. Most of these wor the greyed finish. Not many Grade II rifles were signed. Engraving coverage is about 50%. The stocks were checkered 22 lines per inch.
Grade III. Originally had on the right side three ducks being chased by what appears to be a setter in a woods scene. The left side has a dog and three pheasants surrounded by grass or some other foliage. The top of the receiver has a spanial type dog with a rabbit in its mouth surrounded by oak leaves and scroll. Coverage is about 95%.
In 1963 this grade was also changed slightly. The dog appears to have a duck instead of a rabbit. Dog is unchanged. From the first year of production until about 1965 they wore the coin finish. After 1965 they had the greyed finish. The wood is skip checkered about 2 lines to the inch.
All triggers on both grade were gold plated. Most Grade III were signed after the first two years of production. There were slight variations in these rifles so the descriptions may be off a bit. The barrels, markings, stock finish and dimentions for all three grades were common to all.
Hope this answers your question.
PS: This information comes from Matt Eastman's book " Browning, Sporting Arms of Distinction"